The field of the invention relates to nuclear waste and more particularly to methods of measuring the radioactive content of nuclear waste containers.
Since the advent of the nuclear age, the presence of nuclear waste has become a significant roadblock to further development of nuclear technology. In the last fifty years, vast amounts of nuclear waste have accumulated.
Nuclear waste is different than other types of waste in that it can kill without direct contact through the effects of radiation. Because of radiation, nuclear waste must be either shielded or stored in protected areas.
While shielding is effective, the added weight creates additional difficulty in storing and moving waste containers. It also adds to the bulk of storage containers.
When nuclear energy first became a factor during World War II (and to a lesser extent even now) nuclear waste was handled in a manner similar to other wastes. In some cases nuclear waste was handled informally with no documentation whatsoever.
What makes nuclear waste more difficult to process than other wastes, however, is the difficulty of identifying and classifying the contents of nuclear waste containers. Every risk associated with chemical and biological waste applies to nuclear waste, with the added factor of the health risks associated with radiation.
In the past, the accepted method for measuring a quantity of a radionuclide within a container has involved the analysis of the entire contents of the container. The analysis of the entire container has been found necessary because of the occasional presence of shielding materials within the container.
Since WWII hundreds of thousands of nuclear waste containers have been filled and stored in a limited number of locations with limited or no regard to what such containers have stored inside them. In order to resolve the problem of nuclear waste, an effort must be made to characterize nuclear waste as a first step in finding a final solution to the disposal of such waste. Accordingly, a need exists for a safe and reliable means of quantitatively measuring the emitted gamma radiations from the nuclear waste within waste containers.
A method and apparatus are provided for assaying a waste container. The method includes the steps of forming a plurality of slices through a volume of the waste container, performing a relatively fast passive prescan to measure a level of gamma-ray radioactivity of each of the plurality of slices and identifying at least some slices of the plurality of slices having a relatively high level of gamma-ray radioactivity. The method further includes the steps of determining a passive assay time for the identified slices based upon the measured radioactivity. A relatively slow passive scan may then be performed of the identified slices based upon the determined passive assay time to quantify a source of the measured gamma-ray radioactivity by weight.